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Full text of "Handbook Of Chemical Engineering - I"

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CHEMICAL ENGINEERING
FIG. 9.—Wickes boiler.
flat surfaces should be one that will give warning of impending failure. Good circulation of water and gases is important. Water should be introduced at a cold point, high up. Gases should be repeatedly conducted across heating surfaces and gas passage areas should gradually contract from furnace to stack. Almost any type of boiler may be so proportioned as to operate at good evaporative efficiency. The Massachusetts Boiler Law and the A. S. M. E. Code are good guides for boiler construction.
Horizontal Tubular Boiler.—This is a cylindrical shell with longitudinal tubes of small diameter through which the gases pass forward after having moved under the shell rearward. A brick setting and a cast-iron front are required.
The uptake may be taken from either the front or rear of the casting, giving the "extension" or "flush" front construction. The former saves floor space. Space should be left behind boilers for access to blowoff cocks, and space also left (preferably in front) for removal of tubes and their replacement.
The thickness t (inches) of shell for a working pressure of p (pounds per square inch) is given by t = aDp ~ 2T, where T = tensile strength of plate, pounds per square inch; D = shell diameter, inches; a = factor of safety divided by efficiency of longitudinal-riveted joint. Thicknesses are rarely below % in. for small boilers or